The present invention relates generally to the field of wireless communications and, more particularly, to shortening call-setup time in wireless communication systems that page call participants.
Many battery powered communication units have a sleep mode in which they are able to conserve power by powering down components such as their receivers. These communication units then xe2x80x9cwake upxe2x80x9d periodically to determine if any messages (pages) are going to be transmitted to them. If there are no messages that the communication unit needs to receive, it will power down in order to extend its battery life. Next generation Code-Division Multiple-Access (CDMA) cellular communication systems, more commonly referred to as CDMA 2000 or Wideband CDMA systems, incorporate such power saving techniques. Each communication unit within a CDMA 2000 system is normally able to determine to which group of four, 20 millisecond (ms), synchronous frames on its paging channel (PCH) it is assigned. This group of frames, referred to as its xe2x80x9cpaging slot,xe2x80x9d is used by the infrastructure to transmit messages to the particular unit. Thus, a communication unit in so-called xe2x80x9cslotted modexe2x80x9d operation exits its sleep mode in order to monitor transmissions associated with its assigned paging slot. The more quickly a communication unit can determine that it has no messages or no more messages to receive, the more quickly it can return to sleep mode and conserve power, further extending its battery life.
CDMA 200 also incorporates a Quick Paging Channel (QPCH) to reduce the time a communication unit must monitor the PCH. QPCH slots comprise four, 20 millisecond (ms), synchronous frames. However, QPCH frames are transmitted 100 ms earlier than their corresponding PCH slot. A couple of paging indicator bits are transmitted in the QPCH slot that tell each communication unit whether it may be addressed by any of the upcoming PCH messages. Because the QPCH does not employ error correction coding or interleaving as the PCH does, the time required for a communication unit to receive and process its bits is small compared to the time required to monitor the PCH slot. Thus, the QPCH allows communication units to determine whether they need to monitor the upcoming corresponding PCH slot at all. Normally, a large number of communication units determine, based on the QPCH indicators, that they do not need to monitor the PCH during the upcoming corresponding slot and they can rapidly re-enter a xe2x80x9csleep mode,xe2x80x9d where battery power is conserved.
While the QPCH enables communication units to save battery life, it also introduces 100 ms of delay (on average) to call-setup time. For dispatch calls, however, call-setup time is very important. A dispatch user expects to xe2x80x9cpush-to-talkxe2x80x9d and begin conversing with other call participants in a very short period of time, usually 1 second or less. Thus, a communication unit, a communication infrastructure, and method that shorten this call-setup time while still providing the benefit of the QPCH are needed.